chrono glibc '-' ext applies to following components within a spec

[durka]

In the latest version, @ShawnZhong implemented #2959 via #3271. This allows the use of - as a modifier in chrono format specs to omit the leading zero from H, M, and S.

However, a difference from std::strftime is that the modification "sticks" to an entire format spec, so {:-M:%S} behaves differently than {:%-M}:{:%S} (the former strips the leading zero from minutes and seconds, while the latter only modifies the minutes). Is this intended behavior?

Here is a godbolt repro.

As a side note, unless I missed it the - extension for chrono specs is not mentioned in the documentation.

[phprus]

Fix: #3812

[durka]

That was fast!

[phprus]

@durka
Please, test this PR